Material flowing from the hopper of a broadcast spreader strikes a rotating impeller or distribution plate positioned therebelow and is distributed by the impeller in a generally fan-shaped, bilaterally symmetrical pattern ahead of the spreader. This relatively expansive distribution pattern permits rapid coverage with a variety of materials ranging in size from powdered forms to pellets. However, since the fertilizer or other material is, in effect, launched from the apparatus, it is sometimes difficult to control the distribution pattern. It is, for instance, difficult to apply a sufficient amount of material to those portions of a lawn that border flower beds, shrubbery, patios and driveways without depositing a substantial amount of material on these outlying areas. This problem is particularly significant where fairly large sized pellets or pearls of fertilizer are being applied. This material is relatively expensive, so the cost of the overspray may be significant. In addition, such pellets contain a substantial amount of material and can damage plant life for which they are unsuitable. Control problems can also arise because substantially different distribution patterns are created by differently sized and weighted particles. Heretofore, if the operator wished to compensate for these changing patterns, the speed and/or course of the spreader over the lawn had to be altered whenever differently sized materials were applied. Accordingly, if it were possible to adjust or modify the distribution pattern of material coming off of the impeller, more uniform applications could be made, and outlying areas could be avoided.
One possibility for controlling the distribution pattern is to provide a deflector that redirects some of the material after it is ejected from the impeller. U.S. Pat. No. 4,511,090 issued Apr. 16, 1985 to Morgan discloses a broadcast spreader provided with a curved deflector that is positioned to block material from reaching beyond one lateral side of the spreader, thereby avoiding outlying gardens, walkways, etc.. While it assists in keeping material within the confines of a yard, the Morgan deflector creates a nonuniform distribution pattern.
Another possibility for controlling the distribution pattern is to change the target area of the impeller that receives material from the hopper. U.S. Pat. No. 4,497,446 issued Feb. 5, 1985 to van der Lely et al discloses a broadcast spreader wherein the drop point or target area on the impeller can be rotated or adjusted annularly. By doing so, the entire distribution pattern is shifted laterally in one direction or the other, depending upon the direction of rotation of the impeller. While the concentration of material in this pattern is substantially uniform, the shift in direction of the entire pattern would tend to throw an excessive amount of material onto areas that were covered before the shift took place.
Departing from the teachings of Morgan and van der Lely et al, the present inventors noted that the distribution pattern could be altered by moving the drop point or target area on the impeller radially inwardly and outwardly. They found that by moving the outer edge of the target area inwardly while keeping the inner edge the same, that a portion of the distribution pattern disposed laterally outwardly from one side of the spreader would be eliminated. The rest of the pattern, however, would remain substantially the same. In this manner, outlying gardens could be avoided without destroying uniformity in the quantity of material being applied from swath to swath.